Helicity amplitudes for the small-angle lepton pair production in e+e- or collisions E.A. Kuraev, A. Schiller, V.G. Serbo and D.V. SerebryakovaEur. Phys. J. C, 4 4 (1998) 631-639DOI: https://doi.org/epjc/v4/p631(epjc814)